[Coco] Replacing Dynamic RAM with Static RAM

[Stephen Adolph]

I have a large quantity of 1M x 16 3.3 V SRAM chips, and a large
quantity of CPLDs.

These parts are perfect for such a card.



On Fri, Jun 11, 2010 at 3:06 PM,  <sales at gimechip.com> wrote:
> I just noticed the mention of using a single 2-Meg SRAM. That's what I've
> been working on, but the SRAM is 1024x16 for a total of 2-Megs by eight. The
> GIME has a 16-bit databus (sort of). Even bytes are in one bank and odd
> bytes in the other, thus a 16-bit SRAM or two 8-bit SRAMs are ideal. It can
> be done with an 8-bit wide SRAM as well, I suppose, but I haven't tried that
> yet.
>
> I am using a 16x4-bit RAM array with associated multiplexing circuits to
> extend the MMU registers by 8-bits.
>
> Since I'm using Static RAM, no modified refresh is required, plus if the
> SRAM is battery backed, the various RAMdisk software can be non-volatile
> (although some of the RAMdisks initialize the disk automatically - that
> behavior would have to be patched out)
>
> The video can only exist within a 512K block - this is a GIME limitation.
> Using Tony's method, a register holds the Video Bank data. During a video
> cycle, the video bank data is presented to the RAM to select 1 of 4 of the
> 512K banks for video.
>
> The CPU, however, can access the entire 2-Megs via the normal paging method.
> During a CPU cycle the DAT register addresses are presented to the Static
> RAM.
>
> There's a little bit more to it than that (for example, the dual WE* signals
> must be accounted for - I've done this by multiplexing them and using A0 to
> select which one passes to the SRAM for R/W* control - A0=0=even bank,
> A0=1=odd bank). This should be completed soon. I'll upload everything to
> coco3.com and maltemedia for any who want to make use of it.
> J&R
>
> ----- Original Message ----- From: <sales at gimechip.com>
> To: "CoCoList for Color Computer Enthusiasts" <coco at maltedmedia.com>
> Sent: Friday, June 11, 2010 1:50 PM
> Subject: Re: [Coco] Replacing Dynamic RAM with Static RAM
>
>
>> Yes, that's what these were for, but I also uploaded a file that uses a
>> 256Kx16 SRAM for the CoCo3 for 512K. It needs a bit of work. It's here:
>> http://www.coco3.com/community/2010/06/512k-simm-and-sram-files
>>
>>
>> ----- Original Message ----- From: "Stephen Adolph" <twospruces at gmail.com>
>> To: "CoCoList for Color Computer Enthusiasts" <coco at maltedmedia.com>
>> Sent: Friday, June 11, 2010 1:21 PM
>> Subject: Re: [Coco] Replacing Dynamic RAM with Static RAM
>>
>>
>> Interesting.
>> I've got a background activity thinking about how to use a single 2MB SRAM
>> chip.
>> Seems that this is a way to replace each individual DRAM with an SRAM.
>>
>> Similar, yet different. hmm more thinking.
>> Steve A
>>
>>>> On 6/11/2010 8:57 AM, sales at gimechip.com wrote:
>>>>>
>>>>> Over the past year, I've had some success at replacing DRAM with SRAM.
>>>>> I
>>>>> have posted some of the schematics and designs to CoCo3.com in these
>>>>> threads:
>>>>>
>>>>> http://www.coco3.com/community/2010/05/512k-upgrade-question
>>>>>
>>>>>
>>>>>
>>>>> http://www.coco3.com/community/2010/06/4164-dram-sram-replacement-1-by-jr-of-gimechip-com
>>>>>
>>>>>
>>>>>
>>>>> http://www.coco3.com/community/2010/06/4164-dram-%E2%80%93-sram-replacement-2-by-jr-of-gimechip-com-c19-march-2010
>>>>>
>>>>> It is relatively simple to demultiplex the multiplexed address lines
>>>>> and
>>>>> to replace DRAM with SRAM. The above links should provide a great deal
>>>>> of
>>>>> information on how I've gotten it to work.
>>>>>
>>>>> As soon as I get the rest of my documents together on the 512K, 1M& 2M
>>>>> CoCo 3 Static RAM upgrades, I'll get those posted as well. -J&R
>>>>>
>>>>> --
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>>>>> Coco at maltedmedia.com
>>>>> http://five.pairlist.net/mailman/listinfo/coco
>>>>>
>>>>>
>>>>
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